A long while back, I stopped buying alkaline batteries. I hate alkalines. They are little time bombs, only instead of going bang, they start leaking, and in so doing, corroding every contact and switch, every bit of circuitry, every thread of anything threaded. Here's a photo of one of the house's clocks -- still working, despite all the leakage. You just never know if your light has been destroyed until you take it apart and find it such.
I started getting serious about being lit properly after a late evening trip home. It was only a couple of miles, but I had no light, and someone very nearly left-crossed me. Of course I was at fault, but at the time I neither knew the rules nor had the money to buy any light, let alone a good one. But so began the quest to put and keep a functional light on my bike, front and rear.
Long ago, I lost count of the failed attempts. I will, however, try to inventory what I do have now, and what it cost me. If you have a C-note, this would be a good place to spend it to get one bike lit properly.
* Pack of four rechargeable AA cells, plus recharging unit ($20)
* Pack of four rechargeable AAA cells, plus recharging unit ($20)
* Planet Bike Superflash taillight ($35)
* Planet Bike Beamer 3 headlight ($25)
That's $100, roughly. One charger goes to work, the second stays home. Two of the AAs go in the light, the other two go in your toolbag. Two of the AAAs go in the taillight, the other two in the bag.
About once a week, depending on how much night riding you do, switch out the pairs in use for the others, and put the depleted ones on the charger.
In actuality, I employ far more than the above. I have two headlights, and three taillights. One of those taillight sets is clipped to my helmet. One of the headlights is an older but very bright model which requires a heavy battery pack, and must be plugged in every couple of days. They make newer, brighter, much lighter light systems; buy them if you can afford to.
Do not skimp on lights, though. If you cannot afford the $100 up front, plan to spend $15 to $25/month until you do have all the pieces you need.